The plasma membrane of every cell serves as a signaling hub, controlling the flux of information across it. As part of the membrane, phosphatidylinositol phosphates (PIPs) are lipid second messengers and are involved in almost all facets of cell physiology, including synaptic transmission, cell proliferation, cell differentition, migration and many others. Their concentrations are tightly regulated by a series of kinases and phosphatases. One such phosphatase, PTEN, is one of the most frequently mutated genes in sporadic human tumors with mutations occurring in glioblastomas, lymphoma, thyroid and melanomas. When PTEN is not functioning properly, PIP levels increase and could activate out of control growth and migration. While cancer is the most commonly cited, several human diseases are linked to PIP metabolizing enzymes such as peripheral neuropathy, Alzheimer's, autism and bipolar disorder. As a result, the proteins regulating PIP signaling have been extensively studied. The voltage sensing phosphatase (VSP) is homologous to PTEN and is a new member of the large class of proteins that regulate the membrane concentrations of PIPs. Classically, PIP regulating enzymes are cytosolic. VSP, on the other hand, is an integral membrane protein and is activated by voltage. The discovery of VSP reveals a gap no one knew existed because voltage regulation of PIP regulating proteins has not been considered. Understanding the effect of VSP on PIP regulatory pathways is crucial because those pathways are fundamental to understanding cells and their signaling. ! This project has the long term objective of probing the molecular mechanism and physiological roles of VSP. To address this long term goal, the immediate specific aims target factors that activate VSP such as lipids. Many membrane proteins are modulated by the lipid composition in the membrane. The expectation that VSP is also modulated by lipids is not unusual. What makes VSP more complicated than a regular membrane protein is the fact that VSP will change the concentrations of those same lipids. This could result in an internal feedback loop causing VSP to essentially self-regulate. This is critical because while other kinases and phosphatases exist to maintain PIP concentrations, those mechanisms may be slower than voltage activation. This proposal will expand our understanding of VSP on a molecular level and how it fits into the broader PIP signaling pathway.